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virtio_ring: use virt_store_mb 

We need a full barrier after writing out event index, using
virt_store_mb there seems better than open-coding.  As usual, we need a
wrapper to account for strong barriers.

It's tempting to use this in vhost as well, for that, we'll
need a variant of smp_store_mb that works on __user pointers.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
This commit is contained in:
Michael S. Tsirkin 2015-12-17 12:20:39 +02:00
parent 9e3f84ce41
commit 788e5b3a5d
2 changed files with 20 additions and 6 deletions
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15
drivers/virtio/virtio_ring.c
View File

@ -517,10 +517,10 @@ void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len)
/* If we expect an interrupt for the next entry, tell host
* by writing event index and flush out the write before
* the read in the next get_buf call. */
if (!(vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT)) {
vring_used_event(&vq->vring) = cpu_to_virtio16(_vq->vdev, vq->last_used_idx);
virtio_mb(vq->weak_barriers);
}
if (!(vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT))
virtio_store_mb(vq->weak_barriers,
&vring_used_event(&vq->vring),
cpu_to_virtio16(_vq->vdev, vq->last_used_idx));
#ifdef DEBUG
vq->last_add_time_valid = false;
@ -653,8 +653,11 @@ bool virtqueue_enable_cb_delayed(struct virtqueue *_vq)
}
/* TODO: tune this threshold */
bufs = (u16)(vq->avail_idx_shadow - vq->last_used_idx) * 3 / 4;
vring_used_event(&vq->vring) = cpu_to_virtio16(_vq->vdev, vq->last_used_idx + bufs);
virtio_mb(vq->weak_barriers);
virtio_store_mb(vq->weak_barriers,
&vring_used_event(&vq->vring),
cpu_to_virtio16(_vq->vdev, vq->last_used_idx + bufs));
if (unlikely((u16)(virtio16_to_cpu(_vq->vdev, vq->vring.used->idx) - vq->last_used_idx) > bufs)) {
END_USE(vq);
return false;

11
include/linux/virtio_ring.h
View File

@ -45,6 +45,17 @@ static inline void virtio_wmb(bool weak_barriers)
wmb();
}
static inline void virtio_store_mb(bool weak_barriers,
__virtio16 *p, __virtio16 v)
{
if (weak_barriers) {
virt_store_mb(*p, v);
} else {
WRITE_ONCE(*p, v);
mb();
}
}
struct virtio_device;
struct virtqueue;